PCMs for Air-Conditioning, Refrigeration & Cold Storage

 

Phase Change Material PCM.

 

Phase Change Materials (PCMs) are "latent" thermal storage materials. They use chemical bonds to store and release heat. The thermal energy transfer occurs when a material changes from a solid to a liquid or from a liquid to a solid form. This is called a change in state or "phase." Initially, these solid-liquid PCMs perform like conventional storage materials; their temperature rises as they absorb solar heat. Unlike conventional heat storage materials, when PCMs reach the temperature at which they change phase (their melting point), they absorb large amounts of heat without getting hotter. When the ambient temperature in the space around the PCM material drops, the PCM solidifies, releasing its stored latent heat. PCMs absorb and emit heat while maintaining a nearly constant temperature. Within the human comfort and electronic-equipment tolerance range of 20°C to 35°C, latent thermal storage materials are very effective. The main applications for PCMs are when space restrictions limit larger thermal storage units in direct gain or sunspace passive solar systems. Phase Change Materials may be used in Thermal Enclosures like Telecom Chambers BTS or BT Shelters or solar domestic hot water heating or passive solar space heating/cooling systems. They are also useful for equalization of day & night temperature and for transport of refrigerated products.

Glauber's salt, Soda ash, Sodium Acetate and paraffin wax are the most commonly used PCMs in solar heating systems. Although these compounds are fairly inexpensive, the packaging and processing necessary to get acceptable performance from them is complicated and costly. They are not offering a reliable pattern of releasing heat as the chemicals in these PCMs separate and stratify when in their liquid state. These PCMs have not always re-solidified properly. When temperatures dropped, they did not completely solidify, reducing their capacity to store latent heat. These problems have been addressed by packaging phase change materials in thin or shallow containers and by adding clumping agents. Many salt hydrate PCMs have the disadvantage that during extraction of stored heat the material super-cools before freezing. This reduces the utility of the materials and if too severe, it can completely prevent heat recovery. They lose their heat storage property after some cycles. These types of PCMs, however, compare unfavorably with the newer generation of low-cost, highly efficient PCMs. Researchers now label these older compounds as "limited utility" PCMs. Phase Change Materials perform best in containers that have a depth of one inch (25.4 millimeters). However, our T-Series Latest™ PCMs have defied this restriction. The packaging material should conduct heat well; and it should be durable enough to withstand frequent changes in the storage material's volume as phase changes occur. It should also restrict the passage of water through the walls, so the materials will not dry out. Packaging must also resist leakage and corrosion. Aluminum, steel and polyethylene are common packaging materials.

We cannot help making a negative comment on the products offered by other brands. Most of the brands are offering Thermal-Salt 29 that freezes at less than 18^oC, making them practically useless in tropical regions. The shelf life of some of the vendors is hardly 45-60 day, making its use by long distance importers almost impractical. Most of such vendors are not manufacturer of the major ingredients but only compounders. Often, they are one-man-show manufacturers and quote fancy prices for the product and demand a fortune for a sample. With the information technology to their aid, they make fancy web sites and manage to squeeze the buyers. We have six manufacturing units, owned and managed by family members and most of the ingredients are manufactured by us.

Phase Change Materials, PCMs Used in Air Conditioning

Latest 29T: Phase Change Material, PCM Latest^TM Brand with Melting Point 29°C and Latent Heat of fusion 175 K.Joule/Kg or 255 K.Joule/liter. It is best suited for Air-Condition Back-up to BT Shelter or Telecom Shelter. It is also a good alternative to bear with when temperature changes from 15°C at night and rises to 40°C in the day. This will act as a heater at night and a cooler in the day.

Latest 22T: Phase Change Material, PCM Latest ^TM  Brand with Melting Point 22°C and Latent Heat of fusion >175KJoule/Kg or 255 K.Joule/liter). It is best suited for Free Air-Conditioning in an area where day and night temperature difference permits it. The material can be placed in an external heat exchanger or in the false ceiling and/or partition walls.

 

Back-up Air-conditioning with Latest™29T PCM

Power Failure is very common in developing countries. The following write up is talking about Telecom Shelters, though it is applicable to any other shelter like site office or Polymer wall-paneled room. It can easily provide human-comfort level, almost through out the day.

Most BT Shelters or Telecom Enclosures are equipped with Electronic Equipments and Battery for emitting proper signal to the cell-phone users. When the power fails, the temperature inside the BTS start rising very rapidly due to heat generated by the equipments and also due to ambient conditions. Diesel Generators are provided to give back up. However they are largely depended on the alertness of the watchman cum operator at the site. The contractors often delay in sending diesel aggravating the problem. To minimize the dependence on generators, Back-up air-conditioning may be provided by phase change material. Latest™ 29T is used in India for giving back-up to Air-Condition. 240kg of Latest™29T is generally used per BTS. 240kg*175 J/kg 42000 K Joules of backup.  This is equal to 42000/3600 = 11.6 KWH of energy (Theoretical Latent Heat of .Latest™29T is 188 KJ/Kg i.e. 12.5 KWH of Energy).

In case of inhabited rooms or offices human comfort level can be achieved by using an External Heat-Exchanger with an inverter switched fan or by using PCM in wall-panels and ceiling.

 

 

TECHNO-COMMERCIAL STATEMENT OF PCM PRODUCT T-series Latest™

Latest™ 25T, Latest™ 20T, Latest™ 18T salts are similar to Latest™ 29T

Phase Change Materials perform best in containers that—when combined with the PCM—total one inch (25.4 millimeters). However, our T-Series Latest™ PCMs have defied this restriction. T-series is the Latest in Phase Change Material-PCM technology, Generation-X. It is not degradable with time. It can be used in thicker layers greater than 1” (> 25mm). This product has made the earlier PCMs obsolete.

 

 

Table of Cycle No. V/s Latent Heat & Sub Cooling for PCM Latest™29T

Cycle No	100	200	300	400	500	1000		1000	1500	2000	1500	2000	2500	3000
Latent Heat KJ/Kg	196	188	188	192	185	178		178	175	170	172	175	178	170
Sub Cooling oC	0.5	1.0	0.9	0.8	0.7	1.0		1.0	1.1	1.2	1.3	1.2	1.3	1.4

The measurement error in Latent Heat can be upto 5% and the Thermometer sensor can be off by 0.5^oC

 

 

Thermal Salt Latest™29T

Our Thermal Salt Latest™29T is a mixture of several ingredients. Most of these items are manufactured by us or by our sister concerns. Its properties are as under:

 

Specific Gravity                        :           1.5

Freezing Point                           :           28^oC

Melting Point                            :           29^oC

Latent Heat of Fusion               :           >175 K.Joule/Kg (40 K. Cal/Kg). 255 K.J/ltr (60000 K.Cal/Cu.m)

*Most manufacturers report the heat of fusion in a temperature range, like 20^oC to 35^oC. The specific heat of PCM in this range will get added to the values. For this temperature range

*Latent Heat of Fusion             :           210 K.Joule/Kg (50 K. Cal/Kg).

Shelf Life                                  :           Infinite

Max. Operating Temp.             :           100^oC

 

For Advanced Users: Most PCM users are at the elementary stage of using the PCMs. They are ordinarily not conditioned to talk of any deviations from the systems, they have heard of. Using PCM-29 itself is more than adequate mental kick for them. Some vendors manage to convince them that the use of PCMs will save energy charges for them. The primary purpose of the PCMs is to provide a back-up to ACs and avoid the use of Diesel Generator. The site managers and the watch-man cum operator of the site may not be sufficiently professional. They often fail to keep the diesel at site and restore to "Keep the Door Open for Cooling" ways to cut corners. The relevance of PCMs is more, if the power failure is a norm in the area of usage. We have a Brain-Wave. Instead of giving 4-6 hours of Back-up, why not give 12-18 hours of Back-up and eliminate the Diesel Generator???!!! This will of course need a better battery capacity.

 

 

 

Free Cooling for a Hall in Bangalore with Latest™21T

PROPOSAL FOR FREE AIR CONDITIONING OF HALL FOR 1000 HOURS/YEAR

Preliminary/Concept Presentation for Data Exchange and Technical Interaction.
Data Offered by the User:
Air Condition Load is 932 Tons of Refrigeration.						932	Tons AC
Carpet Area of the Hall is 200000 sq ft.						200000	Sq.ft
Comfort Level is 23oC. [Phase Change Material (PCM) to start Melting at 21oC						21	oC
No. of people is 1800						1800	Ppl
We get 19oC for at least 4hr/night for hundred nights in a year
Fan use is permitted

 

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